This invention relates to improvements in devices for dispensing a measured volume of liquid and is particularly concerned with such dispensing devices as are used for dispensing hot water in coffee-making machines.
Such dispensing devices generally comprise a double-acting piston which is reciprocable in a cylinder to which water is pumped to one side of the piston so that the latter is displaced by the water from an initial position against the effect of a return spring. During this stroke of the piston water which has been transferred from the one side of the piston to the other is expelled from the cylinder to a filter carrying cup to make coffee. The piston carries a piston rod which extends externally of the cylinder and which, after a predetermined displacement of the piston from the initial position, actuates an externally located microswitch to switch off the pump and hence stop the supply of water to the cylinder, thereby limiting the stroke of the piston and controlling the quantity of water supplied to the cylinder. The position of the microswitch is adjustable so that by adjustment thereof, volume of water dispensed may be controlled. When the microswitch is actuated, the supply of water from the cylinder to the filter carrying cup ceases to discontinue the infusion stage and the filter carrying cup is placed in communication with the atmosphere so as to obtain a partial drying of the coffee grounds by decompression.
In such known devices, the water, usually hot water, is fed to the cylinder at a pressure approaching 9 atmospheres and packing is required to seal the piston rod which extends externally of the cylinder. Such packing usually has a limited life and is expensive to provide and replace.
It is an object of the present invention to provide an improved device for dispensing a measured volume of liquid, particularly hot water for a coffee-making machine, in which the disadvantages of the known devices referred to above are substantially eliminated.
It is a more particular object of the present invention to provide an improved device for dispensing a measured volume of liquid, particularly hot water for a coffee-making machine in which the necessity for a packing to seal a piston rod associated with the dispensing cylinder is entirely removed.